More and more firms, but also private individuals, are installing alternative energy sources, such as wind turbines or photovoltaic devices, on the premise of their buildings or attached to the buildings themselves, for example on their roofs. Such energy sources may be used to satisfy their own needs for electrical power, and in addition to feed excess electrical power produced by the alternative energy source to the external power grid. When installing an alternative energy source, usually, an energy storage device is also installed at the site to store some of the excess electrical energy provided by the alternative energy source in order to utilize the stored energy at a different time. For example, on very sunny days, a photovoltaic device might produce much more energy than can be consumed by the user. This excess energy may be partly used to charge the energy storage device, such as a battery system, and partly fed into the external power grid. During the night, or on less sunny days, when the electric power produced by the photovoltaic device is not sufficient for the user's needs, the energy stored in the energy storage device may be utilized to power the building either exclusively or in addition to energy taken from the external grid.
An energy supply system providing such an energy storage device is usually very complex. This is because the wiring of such an energy storage device to the in-hose electric grid and to the external power grid through the building connection box can be quite intricate. There is the danger of accidentally feeding electrical energy either from the alternative energy source or from the energy storage device into the external power grid in an undesirable way or at an undesirable time when the wiring is not done properly. In other cases, a badly wired system might damage or even destroy components of the energy supply system. Furthermore, to ensure proper wiring and setup, the system becomes expensive.
It is the object of the present invention to overcome these disadvantages and obstacles and provide for a more reliable energy supply system, which is simpler and more cost effective to set up.